The reasons for the GOP advantage are pretty straightforward. Midterm elections are usually poor for the president’s party, and the Senate contests this year are in states where, on average, President Obama won just 46 percent of the vote in 2012.1 Democrats are battling a hangover effect in these states, most of which were last contested in 2008, a high-water mark for the party. On the basis of polling and the other indicators our model evaluates, Republicans are more likely than not to win the six seats they need to take over the Senate. This isn’t news, exactly; the same conditions held way back in March.
An equally important theme is the high degree of uncertainty around that outcome. A large number of states remain competitive, and Democrats could easily retain the Senate.